Testing of foundry sand



y 29, 1969 .1. M. MACNAIR 3,

TESTING OF FOUNDRY SAND Filed Feb. 14, 1966 lwvewron. Joa-m Mu. MACNMR ATTYS.

United States Patent 3,457,769 TESTING OF FOUNDRY SAND John Miles Macnair, Nechells, Birmingham, England, as-

signor to Foseco Technik Limited, Nechells, England, a British company Filed Feb. 14, 1966, Ser. No. 527,304 Claims priority, application Great Britain, Feb. 17, 1965, 6,894/ 65 Int. Cl. GOln 25/00 U.S. C]. 73-15 3 Claims ABSTRACT OF THE DISCLOSURE A method for testing the propensity of a foundry moulding sand to spall which includes compacting a sand sample having a particular predetermined moisture content to a shape having a flat surface, facing the flat surface downward at a preselected distance from a source of radiant heat at a temperature sufiicient to cause spalling in a standard moulding sand under the conditions and determining the time before spalling occurs and the extent thereof.

This invention relates to a method of testing foundry sands and more particularly to a method of testing the propensity of a foundry sand to spall in use, giving rise to the phenomenon known as scabbing.

A so called green sand moulding mixture comprises natural or synthetic quartz or sand particles held together by a mixture of clay and water. The clay can be either a naturally occurring impurity in the sand as excavated or an added material such as bentonite. The clay and a definite amount of water are dispersed round the sand grains by a milling process and the resulting mixture, which is the moulding material, can be compacted by ramming to enable it to withstand compressive and tensile forces. After the moulding mixture has been moulded it may be baked to expel most of the water present and enable it to be handled and this mould is then ready to be used in a metal casting process or, alternatively, the mould can be used in its green, i.e., unbaked state.

During the preparation of metal casting using green sand moulds, defects due to expansion of the moulds sometimes occur. The worst of these defects is that of scabbing and the mechanism by which this occurs is believed to be as follows. As the molten metal fills the mould it subjects the surface of the mould to intense radiant heat from the molten metal surface, and, because of this, moisture contained in the mould is driven from the surface of the mould into the body of the mould where it recondenses to form a stratum or layer of relatively high moisture content. As the mould surface heats up it expands and because the stratum of higher moisture content tends to be mechanically the weakest plane, the body of sand tends to shear along this plane so that the heated surface shell of the mould bends and breaks away, i.e., spalls. The phenonomenon is most marked on downwardly-facing horizontal surfaces of the mould interior, these being the areas which are subjected to heat radiated from the surface of the molten metal as it rises within the mould.

It is an object of the present invention to provide a method of testing foundry sands, within which term is included mixtures of foundry sands with antispalling or other additives, to obtain a measure of the tendency of the foundry sand to spall.

According to the present invention, therefore, there is provided a method of testing the propensity of a foundry moulding sand to spall, which comprises compacting a "ice sample of sand to be tested at a standard moisture content, to a shape having a flat surface and of a thickness greater than any potential thickness of spall, locating the shape with a flat surface facing downwards a preselected distance above a source of radiant heat at a temperature sufficient to cause spalling in a standard foundry moulding sand under the conditions obtaining, and determining the time taken before spalling of the test sample occurs and the extent of spalling in terms of depth and area.

The specific detail of the method, e.g., dimensions of the test sample, the distance above the source of radiant heat and the temperature of that source, may be varied but the following is a most convenient set of conditions for carrying out the process of the test, described in relation to the accompanying drawing.

Referring to the drawing, a sample of the sand mix to be tested is lightly handpressed onto a pattern plate to a depth of 5 cm. in a small moulding box 1, The pattern plate, onto which the test card is moulded, may be either plane or of a suitable design to artifically increase (or diminish) spalling, e.g., a corrugated, grooved or ridged pattern plate. The box 1 is then filled with backing sand, and jolted for 15 seconds. The box is then topped up again and jolted for a further 15 seconds, after which the surplus backing sand is removed and the surface smoothed.

A refractory plate 2 is electrically heated to temperature selected in the range l000 0-1500 C. and thermostatically maintained at the selected temperature. The test surface of the moulded sand 3 is inverted and positioned so that an area of 23 cm. square (529 sq. cm.) of its surface, at a distance of 3.8 cm. above the heated plate 2, receives radiation from the plate in a manner similar to that encountered under casting conditions.

The time is measured between subjection of the test sample to radiant heat and the time wherein spalling first occurs. If no spalling has occurred at the end of 40 seconds the sample sand can be regarded as satisfactory for most foundry mould purposes. Within this period the longer time it takes for spalling first to occur the more resistant to spalling is the test sand when used in foundry practice. Furthermore, the depth and extent of the spalling provides an additional assessment of the susceptibility of the sand to cause casting defects.

In the case of a standard mix of congleton sand containing 4% by weight of bentonite and 3% by weight of water, the foregoing test shows a spalling time of 9 seconds, 48% of the surface being spalled. In 15 seconds of the surface is spalled. By way of comparison the same composition containing 0.5% by weight of a mixture of 91% pregelatinised starch and 9% boric acid as an antispalling agent, when similarly tested, showed a spalling time of 32 seconds, when 35% of its surface was spalled. In 35 seconds, 50% of its surface was spalled. The test thus clearly shows the superiority of the comparison sample in which the antispalling additive was present and this superiority is shown in practice.

The method of the invention closely simulates the conditions which occur in actual practical use of the sand or a sand mould and it is found that the results obtained are consistently reproducible and afford a very sound measure of the propensity of a sand mix to spalling, thus indicating the value of the sand for any particular foundry use.

I claim as my invention:

1. A method of testing the propensity of a foundry moulding sand to spall, which comprises compacting a sample of sand to be tested at a standard moisture content, to a shape having a flat surface and of a thickness greater than any potential thickness of spall, locating the shape with a flat surface facing downwards a preselected distance above a source of radiant heat at a temperature suflicient to cause spalling in a standard foundry moulding sand under the conditions obtaining, and determining the time taken before spalling of the test sample occurs and the extent of spalling in terms of depth and area.

2. A method according to claim 1, wherein the source of radiant heat is an electrically heated plate.

3. A method according to claim 2 wherein the plate is maintained at a temperature of 1000 to 1500 C.

5 JAMES J. GILL, Primary Examiner HERBERT GOLDSTEIN, Assistant Examiner US. Cl. X.R. 

